Large-power electric motors are used in hybrid vehicles and electric vehicles rapidly finding wider use recently, and power converters for driving such electric motors comprise electronic devices such as reactors capable of withstanding high voltage and large current. An electronic device is constituted by a coil device contained in a metal case, the coil device comprising a coil, an insulating resin bobbin around which the coil is wound, and a magnetic core disposed in the bobbin. The metal case is filled with a potting resin (molding resin) for fixing the coil device. The metal case is firmly fixed to metal plates and heat sinks acting as cooling means, frames, circuit boards, etc., which may be called “substrates” in general, by fastening means such as bolts, lest that it is easily detached by the mechanical vibration of vehicles.
Because battery voltage of several hundreds of volts is supplied to the coil, high electric insulation is required between a coil and a core and a metal case to prevent the breakage of the electronic device, or current leak and electric shock. Accordingly, insulating resins such as epoxy resins, silicone resins, etc. are used as the potting resin.
In an electronic device comprising a coil device fixed by a potting resin in a metal case, cracking likely occurs in the potting resin or its boundary with the metal case, because of thermal stress due to thermal expansion difference between the potting resin and the metal case, mechanical vibration applied to the electronic device, etc. As a result, sufficient heat dissipation is not obtained, and the fixing of the coil device is likely damaged.
To cope with such problems, as shown in FIG. 23, JP 2010-34228 A proposes a reactor 500 comprising an assembly 510 comprising a coil 501 and an annular magnetic core 502 supporting the coil 501, a metal case 512 containing the assembly 510, and a potting resin 514 filling a gap between the metal case 512 and the assembly 510; the metal case 512 having an open box shape having a bottom wall and side walls; and inner surfaces of the side walls being provided with raggedness 512a in contact with the potting resin 514. The raggedness 512a on the side walls of the metal case 512 provides a large contact area between the metal case 512 and the potting resin 514, with high adhesion therebetween, so that the assembly 510 is not easily detached from the metal case 512 even if the potting resin 514 is cracked.
In the structure disclosed in JP 2010-34228 A, however, the side walls of the metal case 512 should have large or much raggedness to have higher adhesion between the metal case 512 and the potting resin 514, so that the metal case 512 has a complicated shape, and thus suffers an increased production cost. Because the assembly (coil device) 510 is still fixed by the potting resin 514, solution has not been achieved in the fundamental problems that the cracking of the potting resin 514 and gaps between the potting resin 514 and the metal case 512 deteriorate the fixing of the coil device 510, resulting in reduced heat dissipation.